1. Field of the Invention
The present invention relates to a sheet member, a forming method of the sheet member, and an exhaust gas treatment apparatus using such a sheet member as its holding and sealing member and/or its heat insulating member. Further, the present invention relates to a muffling apparatus having such a sheet member as a sound absorber.
2. Description of the Related Art
The number of vehicles has been dramatically increased from the beginning of this century, thereby steadily and rapidly increasing the amount of exhaust gas exhausted from the internal combustion engines of the vehicles. Particularly, various materials included in the exhaust gas exhausted from diesel engines are responsible for causing contamination, thereby seriously damaging the world-wide environment.
Under such circumstances, various exhaust gas treatment apparatuses have been conventionally proposed and put into practice. In a typical exhaust gas treatment apparatus, there is a casing made of, for example, metal in the middle of an exhaust gas tube connected to an exhaust gas manifold of an engine, and there is an exhaust gas treatment member in the casing. The exhaust gas treatment member has many cells each extending in the longitudinal direction and separated from each other by cell walls. As examples of the exhaust gas treatment member, there are an exhaust gas filter such as a catalyst carrier and a Diesel Particulate Filter (DPF). In such DPFs, one end surface of each cell is sealed to form a checkered pattern and the particulates in exhaust gas can be removed by being trapped on the cell walls before the exhaust gas is exhausted from the exhaust gas treatment member. The typical materials of the exhaust gas treatment member include ceramics in addition to metals and alloys. As a typical example of the exhaust gas treatment member, cordierite honeycomb filter is known. Recently, porous sintered silicon carbide has started to be used as a material of the exhaust gas treatment members from the viewpoint of its properties of thermal insulation, mechanical strength, and chemical stability.
Generally, a holding and sealing member is displaced between such an exhaust gas treatment member and a casing. The holding and sealing member is used to avoid the contact between the exhaust gas treatment member and the casing so as to avoid damage while the vehicle is being operated and also avoid leakage of untreated exhaust gas through the gaps between the casing and the exhaust gas treatment member. Further, the holding and sealing member has a role to avoid the displacement of the exhaust gas treatment member due to the pressure of the exhaust gas. Still further, the holding and sealing member is required to be kept at high temperature to sustain the reactivity, and to have thermal insulation efficiency. As a member meeting the above requirements, there is a sheet member made of inorganic fibers such as alumina-based fibers.
The sheet member is twisted around at least one part on the outer surface excepting an opening surface of the exhaust gas treatment member. For example, one end of the sheet member is engaged with the other end of the sheet member, and the sheet member is integrated with the exhaust treatment member by, for example, taping, so as to be used. After the processes, the integrated parts are housed inside the casing to form the exhaust gas treatment apparatus.
On the other hand, the inorganic fibers included in such a sheet member typically have various fiber diameters including extremely small diameters. Such fine fibers are apt to be scattered in all directions when being handled, so it is difficult to handle such fibers and, therefore, it is not good for the working environment and human health. For example, according to a report, inorganic fibers having a diameter of 3 micrometers or less are not good for human health. Because of the feature, inorganic fibers may be subject to control in some areas (For example, Germany Technical Guideline TRGS905). The contents of Germany Technical Guideline TRGS905 are incorporated herein by reference in their entirety.
To solve the problem, there is disclosed a sheet member that does not include inorganic fibers having a diameter of 3 micrometers or less (see Japanese Patent Application Publication No. 2005-120560).
The contents of Japanese Patent Application Publication No. 2005-120560 are incorporated herein by reference in their entirety.